the thd+N is .0075%, and although it does not specify, its likely at 1khz.
look at the schematic posted above. about 15db of feedback around the grid of the tube. Lowering the input impedance to bipolar levels or lower and kind of negating any possible use of an input tube. Also the plate current source.
spice indicates a second harmonic distortion of -74db at 1khz (.02%) and a 3rd harmonic distortion of -109db (.0003%) at 1khz
however at 10khz the second harmonic is -60db (.1%) and the third harmonic is -96db (.002%)
you can work out the summation on your own.
plus of course the messed up soundstage due to the inverse phase. Something the plankton experts seem to ignore.
In reality, with an old school analog thd meter, the numbers are going to be much much higher.
and of course this is all measured with a 300 ohm resistor. Use a real load especially low impedance, and the numbers go way up.
This amp actually gets nowhere near these numbers in real world testing.
Massdrop Cavalli Tube Hybrid
in Headphone Amplification
Posted
This amp actually gets nowhere near these numbers in real world testing.
https://www.superbestaudiofriends.org/index.php?threads/massdrop-cavalli-tube-hybrid-amp-technical-measurements.5900/
This is for testing at both 300 ohm and 30 ohm. And testing with an LPS (spoiler: THD+N drops even more).